Capsule reskinned with a birthday balloon

[jtmotenz]

Yes, the title is correct. Does it work? No.
But I am calling today a win because now I generally know how to do this. I achieved the critical gap in between the membrane and the backplate, and the tension is close enough compared to my other capsules.
Now I want to build a rig that will let me get the same exact tension, every time, and keep things perfectly aligned throughout the whole process.

I understand that the balloon is wayyyy too thick and not even close to being the right material, but it's all I had laying around. Baby steps.
I used a few large sockets and duct tape to secure the backplate, and a thin cylinder that I covered with the balloon material, tensioned by duct tape once again. I then put the cylinder over the backplate, and used more duct tape to pull the cylinder over the backplate contraption, allowing me to keep constant tension on the membrane.

Oh and I did the unforgivable mistake of puncturing the membrane with a screwdriver... This is why I'm using a balloon and not gold sputtered mylar.

Now I have to find some suitable membrane material and see if this would even work!

ps- I wired it up into a mic, and it responds to wind and taps onto the mic body. I suspect this is only because of the thickness of the balloon material. I think if it was the proper thickness, it would be audible despite only being aluminum... Any thoughts?

 

[k brown]

Actually the balloon is exactly the right material; they are Mylar, the same used in microphones - it's just, as you say, too thick and the aluminization probably also too heavy.

I don't know if it's just me, but I can't get your images to open.

 

[jarvis]

It's kind of hard to tell from the pictures but it looks you are shorting the diaphragm to the backplate. These center terminated capsules usually don't have any metal sputtered where the clamping ring is making contact with the diaphragm to provide isolation. With how you have it set up, it seems like the clamping ring is making direct contact with the sputtered aluminium and shorting it to the backplate via the screws.

Best
Jannis

 

[OneRoomStudio]

It's kind of hard to tell from the pictures but it looks you are shorting the diaphragm to the backplate. These center terminated capsules usually don't have any metal sputtered where the clamping ring is making contact with the diaphragm to provide isolation. With how you have it set up, it seems like the clamping ring is making direct contact with the sputtered aluminium and shorting it to the backplate via the screws.

Best
Jannis

I had the same thought. You might be better off trying an edge-terminated style (you can use the same backplate).

 

[ricardo]

This is why I'm using a balloon and not gold sputtered mylar.

Now I have to find some suitable membrane material and see if this would even work!

Gold has to be sputtered onto pretensioned Mylar. If you don't do this, the gold will crack when you tension the Mylar and you WILL have intermittent & unreliable yuckiness.

Aluminium flashed Mylar is far more forgiving. Go to a model shop with a multimeter and check their Aluminised Mylar is flashed on only one side. Some products have the Aluminium sealed inside so no use to us.

https://micronwings.com/product/mylar-5-micron-aluminised/

This is useful only for edge terminated capsules of course.

I think there is a Neumann (?) youTube video which shows how they tension capsules consistently. If anyone knows where it is, please post. We used the same method at Calrec with slight different jigs.

 

[jtmotenz]

Actually the balloon is exactly the right material; they are Mylar, the same used in microphones - it's just, as you say, too thick and the aluminization probably also too heavy.

I don't know if it's just me, but I can't get your images to open.

It's kind of hard to tell from the pictures but it looks you are shorting the diaphragm to the backplate. These center terminated capsules usually don't have any metal sputtered where the clamping ring is making contact with the diaphragm to provide isolation. With how you have it set up, it seems like the clamping ring is making direct contact with the sputtered aluminium and shorting it to the backplate via the screws.

Best
Jannis

You are correct. This was only a test. I can imagine that It will be hard to get mylar with the sputtering in a focused spot, so maybe I'll have to go with an edge terminated design.

 

[jtmotenz]

Gold has to be sputtered onto pretensioned Mylar. If you don't do this, the gold will crack when you tension the Mylar and you WILL have intermittent & unreliable yuckiness.

Aluminium flashed Mylar is far more forgiving. Go to a model shop with a multimeter and check their Aluminised Mylar is flashed on only one side. Some products have the Aluminium sealed inside so no use to us.

https://micronwings.com/product/mylar-5-micron-aluminised/

This is useful only for edge terminated capsules of course.

I think there is a Neumann (?) youTube video which shows how they tension capsules consistently. If anyone knows where it is, please post. We used the same method at Calrec with slight different jigs.

Thank you. Now how does aluminum perform? It's far less conductive obviously, at what point does this affect the sound?

 

[k brown]

Many fine microphones have aluminized diaphragms; for example, the Oktava MK-012 and the Line Audio Omni1 and CM4.

 

[gyraf]

..you can just remove the aluminum from the area you want without'it. Caustic soda? Some acid?

also, foil from unwinding axial polyester capacitors works, if the foil gets wide enough - i.e. if the axial cap started out long enough. Note that lower capacitor working voltage = thinner foil

 

[jtmotenz]

Many fine microphones have aluminized diaphragms; for example, the Oktava MK-012 and the Line Audio Omni1 and CM4.

Cool to hear, that was my next question.

 

[jtmotenz]

..you can just remove the aluminum from the area you want without'it. Caustic soda? Some acid?

also, foil from unwinding axial polyester capacitors works, if the foil gets wide enough - i.e. if the axial cap started out long enough. Note that lower capacitor working voltage = thinner foil

I've seen 47uF come up for this- maybe this is my next move.